The present invention relates to belt drive systems and more particularly to self-adjusting contact mechanisms for such systems.
Machines have long incorporated belts as transportation mechanisms to move objects. A belt drive system may use surface contact between a belt and a contact surface on each object to transport the object, the drive belt of such a system maintaining frictional contact with the object and/or cogs or other projections may be provided on the contacting surface of the belt which engage mating depressions in the object. In order for contact with each object to be maintained with sufficient pressure to assure frictional engagement and/or to assure mating of a belt projection with an object depression, and thus to avoid slippage, periodic adjustments are often required to accommodate variations in the belt and/or other system components due to factors including, but not limited to, tolerance variations and wear over time.
A contact shoe may sometimes be used to maintain and enhance positioning of the drive belt and engagement between the drive belt and the object being moved, proper adjustment of the contact shoe being required to prolong belt life, minimize positioning xe2x80x9cslop,xe2x80x9d and account for variations in objects being moved. Some such contact shoes are bolted or otherwise secured at a fixed angle/position, thereby providing a force or pressure to maintain contact between the drive belt and the contact surface of the object that may vary with wear and other factors. While these prior contact shoes generally could manually be adjusted with a slotted mounting bracket to set the contact shoe at a fixed position relative to the belt, such shoes are difficult to adjust and position precisely and cannot automatically adapt to changing conditions in the belt system.
Other prior contact shoes have utilized a single helical spring to provide limited control of contact pressure/position between the shoe and belt, for example using the spring provide an adjustable contact force or self-centering contact shoe with variable position to automatically adjust for belt system wear and position over a range of tolerances. Any larger adjustment must be made to the whole shoe. As a result, these devices require frequent, expensive maintenance down time, cannot function over a wide range of tolerances, and unless monitored and manually adjusted at relatively frequent intervals, cannot provide an even force over the shoe against the belt, resulting in slippage and other problems which can impede precise and rapid operation of the belt system.
A need therefore exists for improved drive belt contact mechanism which overcome the various prior art deficiencies indicated above.
In accordance with the above, this invention provides a self-adjusting contact mechanism for a belt system which includes a shoe base having a low friction belt contacting surface, an arm assembly pivotally connected to a stable surface at a first point thereon and having a shoe base attached at a second point thereon spaced from the first point, and a compression mechanism acting on said arm assembly at a contact point spaced from the second point to apply a controlled force to the arm assembly, and through the arm assembly to the shoe base attached thereto, to maintain the low friction surface of the shoe base in controlled force contact with the belt. The compression mechanism may include at least one spring pretensioned to act on the arm assembly at the contact point to bias the arm assembly in a direction to maintain the low friction surface of the attached shoe base in contact with the belt. For at least one embodiment, the contact point is at the first or pivot point and the spring is part of the pivot at such point. Such embodiment may include a tension adjusting mechanism for the spring.
For other embodiments, the arm assembly includes an L-shaped arm, the first point being at an elbow of the arm, the second point being at one end of the arm and the contact point being at the other end of the arm. For this embodiment, the spring may be a compression spring tensioned to apply a force to the arm at the contact point to pivot the arm in a direction to bring the low friction surface of the shoe base attached to the corresponding arm assembly into contact with the belt. The compression mechanism may also include a second compression spring mounted to apply a counterbalancing force to the arm at the contact point to the force being applied by the spring, the force applied by the spring being greater than the force applied by the second spring. The spring and second spring may be selected and pretensioned so that a substantially constant force is applied through the arm and the shoe base attached thereto to the belt regardless of arm position. A pretensioning adjustment may also be provided for at least one of the springs and, more generally, a pretensioning adjustment mechanism may be applied for the compression mechanism. The relative lengths of legs for the L-shaped arm may be selected to achieve a selected mechanical advantage.
The arm assembly may include at least two brackets attached at spaced points along the arm, the first or pivot point being at substantially one end of the each bracket, which end is pivotably connected to the stable surface, and the second point being at substantially a second end of each bracket. The brackets are on opposite sides of the L-shaped arm for at least some embodiments. The second end of each bracket is preferably pivotably connected to the shoe base, permitting the shoe base to pivot to maintain the low friction surface substantially parallel to the belt, the shoe base being pivotably connected to the arm assembly at the second point for all preferred embodiments.
There may be a plurality of shoe bases, each acting at a different point along the belt, there being at least one arm assembly for each shoe base. There may also be a plurality of compression mechanisms acting on each arm assembly and the low friction surface may be removably attached to each shoe base.
In accordance with another aspect of the invention, the self-adjusting contact mechanism for the belt system includes a shoe base having a low friction belt contacting surface, a mount which supports the shoe base with its low friction surface at least adjacent the belt, and a compression mechanism having first and second compression components mounted to provide counterbalancing forces to the mount, and thus to the shoe base, the relative counterbalancing forces of the components resulting in the selected, controlled force profile for the shoe surface against the belt as a function of shoe base position. The force profile may, for example, be a substantially constant force. The compression components may each be a selectively pretensioned compression spring and a mechanism may be provided for controlling the pretensioning of at least one of the springs. The shoe base may also be pivotably connected to the mount to permit the shoe base to pivot to maintain the low friction surface substantially parallel to the belt.
Various embodiments of the present invention provide certain advantages and overcome certain drawbacks of prior devices and systems. Embodiments of the invention may not share the same advantages and those that do may not share them under all circumstances. This being said, the present invention provides numerous advantages including the noted advantage of prolonging belt life and minimizing positioning xe2x80x9cslop,xe2x80x9d variations in different objects, and maintenance down time.
Further features and advantages of the present invention as well as the structure of various embodiments of the present invention are described in detail below with reference to the accompanying drawings.